This invention relates to the recovery of energy from geothermal brines and other hot water sources, and is particularly concerned with a process and system of the aforementioned type, employing direct contact heat exchange between the hot brine or other water containing fluid such as hot water feed, and a working fluid, wherein the heated working fluid is expanded to produce work, and the expanded and discharged working fluid is recycled to the heat transfer column, and further providing for working fluid recovery under conditions to afford minimum working fluid loss and maximum energy extracted from the expander.
U.S. Pat. No. 3,988,895 to Sheinbaum discloses power generation from hot brines by passing a hot fluid in direct contact heat exchange relation with a working fluid. The working fluid is vaporized and the vaporized working fluid is passed through a power extracting gas expansion device.
The prior art has failed, however, to recognize fully the problem of working fluid loss in uncondensible gases which come into the system particularly with the hot brine or hot water and which must be vented. Further, the prior art has not fully appreciated and solved the problem of working fluid loss in exit brine or hot water from the heat transfer column.
In my copending application, Ser. No. 589,068, filed June 23, 1975, there is described a process and system comprising heating the brine or hot water source in a direct contact heat transfer column, and having as an important feature the operation of the heat transfer column at or above the critical pressure of the working fluid, with the hot brine or hot water feed at or above the critical temperature of the working fluid, and converting the working fluid to a dense phase fluid. The heated working fluid is then passed through an expander to produce work, and the working fluid discharged from the expander is cooled and condensed, and such working fluid is separated and pumped back to the heat transfer column to be heated and carried through the cycle repeatedly.
It is an object of the present invention to provide a process and system for recovery of energy from geothermal brines and hot water sources by operation of a heat transfer column providing direct heat transfer between the hot brine or hot water, and a working fluid, under conditions of operation particularly with respect to pressure in the heat transfer column in relation to the critical pressure of the working fluid, different from the critical or supercritical conditions of my above application, yet affording maximum energy recovery for any individual working fluid. A further object is to provide a process and system of the aforementioned type which operates under subcritical pressure conditions with respect to the working fluid in the heat transfer column, in contrast to the critical or supercritical pressure conditions of operation of my above copending application. A further object is the provision in the procedure and system, for removal of working fluid from the exit brine or water from the column and recovery of such working fluid. A still further object is the control of the working fluid concentration in the uncondensible vent gas from the system to obtain an economic balance between energy recovery from the process and system, and working fluid loss in the uncondensible vent gas. Yet another object is to operate under conditions to substantially reduce the quantity of vent gas containing working fluid that vents from the system to thereby minimize working fluid losses, while maximizing energy recovery. Still another object is the provision of simple and efficient procedure for removing the major portion of uncondensible gases from the incoming brine or hot water source prior to introduction into the heat transfer column. Another object is the provision of procedure and system for converting H.sub.2 S in such removed uncondensible gases to sulfur. Another object is to use the H.sub.2 S converting system in conjunction with the above process to also handle condensed water and any vent gas from the accumulator, thus reducing air and water pollution problems and recovering good quality water.